Chagas' disease, caused by the obligate intracellular protozoan Trypanosoma cruzi, is the most important parasitic disease in Latin America, afflicting more than 8 million people, 30-40% of whom have or will develop cardiomyopathy years or decades after the parasite first invades cardiomyocytes during acute disease. The goal of this proposal is to decipher the molecular basis for T. cruzi invasion of cardiomyocytes and gain insight into the symbiotic host - parasite interactions that protect the heart during acute disease and the asymptomatic indeterminate phase, despite persistent parasitism. Preliminary studies suggest that T. cruzi uses its surface ligand PDNF to bind cardiomyocyte receptor tyrosine kinase TrkC, leading to cell invasion. Furthermore, T. cruzi recognition and activation of cardiomyocyte-TrkC induces expression and secretion of nerve growth factor (NGF), a proven repair and injury reversal trigger in nerves of the heart and other tissues, suggesting a mechanism that contributes to damage control in the T. cruzi-infected heart. Lastly, Asp-box motifs in PDNF appear to be involved differentially in parasite invasion and trophic stimulation of host cells. Pursuing these observations, we propose to determine whether and how T. cruzi, via PDNF, 1) exploits neurotrophin receptor TrkC to invade cardiomyocytes; 2) promotes paracrine signaling trough cardiomyocyte-secreted NGF to protect cardiac nerves against injury; and 3) differentially interacts with Trk receptors through Asp-boxes to stimulate either host cell invasio or trophic responses. These studies will employ molecular biology and biochemical methods, immunoassays, cell culture and animal models to achieve the specific aims. In addition, the project may lead to the development of novel, custom-designed, PDNF-based therapeutics to selectively reduce T. cruzi burden in the heart and other Trk-rich organs and, by boosting NGF production, reverse deteriorated heart innervation that results from NGF deficiency.